Interceptor valves, also referred to as intercept valves, or control valves are utilized in steam-cycle, power generation plants, to regulate steam flow into steam turbines. Typically, control or interceptor valves are utilized to throttle, or completely isolate steam flow into intermediate-pressure steam turbines in a steam-cycle power plant. Both control-type or interceptor-type steam valves have the same general construction and features. Further description herein will focus on interceptor-type steam valves, but the same concepts are also applicable to control-type steam valves.
FIG. 1 shows an exemplary, known interceptor valve 10 that is utilized in steam-cycle power plants. The interceptor valve 10 includes a valve casing 12, which defines an internal plenum 14 for passage of pressurized steam from an inlet to an outlet. A valve body 15 throttles steam flow from the inlet through the outlet, by translating within the plenum 14. In FIG. 1, the valve body is in a closed position, which blocks steam flow. An upper end of the valve casing 12 casing defines a casing rim 16 that circumscribes the internal plenum 14. The casing rim 16 includes a counter bore 17 that defines its inner diameter, and an upper surface 18, for opposed orientation with a valve bonnet 20. The valve bonnet 20 retains the valve body 15, and is secured to the casing rim 16 by bonnet bolts 21.
Referring to FIGS. 1 and 2, the interceptor valve 10 retains a valve strainer basket 22 for inhibiting passage of foreign matter or other debris entrained within steam flow from passing through the steam outlet. The valve strainer basket 22 includes a strainer rim 24 having an outer diameter that is slidably nested within the counter bore 17 of the casing rim 16. The strainer rim 24 includes an upper surface 26, which defines opposed, first 28 and second 30 female-threaded apertures. The valve strainer basket 22 has a porous strainer skirt 32 that projects downwardly from the strainer rim 24 into the internal plenum 14 of the valve casing 12. The porous strainer skirt 32 is typically fabricated with an array of piercing through-holes, and is interposed in the steam flow between the inlet and outlet of the valve casing, circumscribing the valve body 15.
Periodically, the valve strainer basket 22 is removed from the interceptor valve 10, to remove accumulated foreign matter from its surfaces and from within the internal plenum 14. During plant operation, foreign matter often accumulates in the circumferential gap between the counter bore 17 of the valve casing 12 and the outer diameter of the nested strainer rim 24, which inhibits slidable, axial separation of the rim from the counter bore. In some operating environments, the valve strainer basket 22, including its strainer rim 24 thermally and/or mechanically deform, creating a tight interference fit between the strainer rim and the counter bore 17, which also inhibits their axial separation during strainer basket removal for maintenance. Typically, strainer baskets 22 have a static weight of 500-1000 pounds (approximately 225-450 kg).
Combination of any or all of foreign matter accumulation, strainer basket 22 deformation, and static lift weight require hoisting equipment to separate the strainer basket 22 from the valve casing 12. In the past, the strainer basket 22 has been coupled to the boom of a lifting crane, such as by threading eye hooks into the opposed, first 28 and second 30 female-threaded apertures formed in the strainer rim 24, or any other coupling features formed in the strainer basket and coupling a lifting sling to both the eye hooks and crane boom. It is challenging to separate the strainer rim 24 from the counter bore 17 of the valve casing 12 with a crane boom, without potentially damaging the strainer basket 22. Additionally, during plant maintenance cycles there are many parallel demands for crane usage.